percentage yeild
4.00g of lawn sand (a mixture of sand and ammonium sulphate) was weighed into a conical flask, and 25 cm3 of 2.0 mol dm-3 sodium hydroxide solution was pipetted into the same flask. The conical flask was boiled for 20 minutes, after which time all the ammonia had been driven off, because: (NH4) 2SO4 (s) + 2NaOH (aq) 2NH3 (g) + Na2SO4 (aq) + 2H2O (1) The residue in the flask was cooled and filtered to remove the sand. The filtrate containing unreacted NaOH was made up to 250 cm3 in a volumetric flask. 25 cm3 samples of this solution were titrated against 0.1 mol dm-3 hydrochloric acid using bromothymol blue as an indicator. HCl + NaOH NaCl + H2O The mean titre was 20.0 cm3. Calculate the percentage of ammonium sulphate by mass in the lawn sand.